Potentiostatic or Galvanostatic EIS? Which one should I use?

How do you choose between potentiostatic and galvanostatic Electrochemical Impedance Spectroscopy experiments?

In general, potentiostatic EIS is preferred because by holding the potential constant, your experiment is performed at a fixed thermodynamic state of your system. However, there are cases where galvanostatic EIS may be a better choice. Several examples of this are high capacity batteries, fuel cells, electrolyzers and, corrosion systems that are drifting. Care should be exercised when using galvanostatic EIS on systems where the impedance changes over several decades between high and low frequencies, for example barrier-coating systems.

In the case of batteries, galvanostatic EIS may be a better choice because of the large currents that are involved with very small changes in potential. Potentiostats are much better at measuring potentials than applying them and for a large battery a small error in the potential application can lead to large DC currents and hence a non-stationary system. By applying a current, your battery can maintain a stable, stationary structure because a small error in applying the current will have little effect.

One concern you may have is whether you will obtain the same results between potentiostatic and galvanostatic experiments. The figure below shows the result of a potentiostatic and galvanostatic experiment on an 18650 Lithium Ion battery. The two sets of data overlay quite well, indicating that either method can be used.

Comparison of Potentiostatic and Galvanostatic EIS Data for an 18650 Lithium Ion Battery

Potentiostatic or Galvanostatic EIS experiments yield identical results especially for low impedance systems like batteries, fuel cells and electrolyzers